"You got a bunch of guys about to turn blue," Charles Duke said at the time

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This photo from 1971 show U.S. astronaut Charles M. Duke, Jr., the Apollo 16 lunar module pilot. Duke, 78, served as Apollo 11's capsule communicator or capcom, as the lunar module descended to the Sea of Tranquility in 1969.

Forty-five years ago Sunday, Neil Armstrong announced that man had reached the moon with the words, "Houston, Tranquility Base here. The Eagle has landed."

Back in Houston, Charles M. Duke Jr. responded, "Roger, Tranquility. We copy you on the ground. You got a bunch of guys about to turn blue. We’re breathing again."

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Duke was so excited he didn’t get "tranquility" quite right -- he later said it came out more like "twangquility." But he stands by the part about turning blue.

"That is the truth," he said this week. "It was so tense. We had had a lot of problems on the descent and so we were very focused on this, the final stages of landing."

Duke, 78, served as Apollo 11's capsule communicator or capcom, as the lunar module descended to the Sea of Tranquility. Armstrong and Edwin Aldrin, known as Buzz, were aboard the Eagle, while Michael Collins remained in orbit.

"We'd had communications problems," Duke recalled. "We had computer overload problems, that gave computer warnings. We had a trajectory that wasn’t correct. Our targeting was wrong and so Neil had to fly over some very rough terrain to get to a suitable landing site, which took a lot more fuel. And so now we're down to the final minute of fuel remaining and so it got very tense as you can imagine at mission control."

Regulations required that the landing be aborted if the fuel went below a certain level, though Duke said he did not believe Armstrong, the mission's commander, would have turned back.

Duke was born in North Carolina, graduated from the U.S. Naval Academy and received a Master's degree from the Massachusetts Institute of Technology in preparation for becoming an astronaut. He later traveled aboard Apollo 16 and was the tenth man to walk on the moon.

Walking on the moon was a ball, he said for a NASA oral history in 1999.

"I found that either the hop or the skip was the best for me," he said. "I put my right foot out front and I just sort of skipped along like that, with one foot out front."

The Kennedy Space Center in Cape Canaveral, Florida, on Sunday will be celebrating the anniversary with special videos and a chance to hear from one of Duke's fellow capsule communicators, Bruce McCandless II. Aldrin has organized a social media campaign, #Apollo45, for the occasion.

Duke, who now lives in New Braunfels, Texas, remembers being intent on making no mistakes during the Eagle's landing.

"Everybody had the attitude, 'if this thing fails, it's not going to be my fault,'" he told NBC.

His team went off duty shortly afterward and he headed home to watch Armstrong's first step on the moon and share his most famous line,"That’s one small step for a man, one giant leap for mankind."